Air intake for free piston engines



Dec. 8, 1 5 w. R. FOIT EI'AL 2,916,026

AIR INTAKE FOR FREE PISTON ENGINES Filed June 23, 1958 5 Sheets-Sheet 1 INVENTORS A TTOE/VE Y Dec. 8, 1959 w. R. FOIT ETA!- 2,916,026

I AIR INTAKE FOR FREE PISTON ENGINES Filed June 23, 1958 v 3 Sheets-Sheet 2 INVENTO RS A TTOPNEY Dec. 8, 1959 Filed June 23, 1958 w. R. Fol T ETA!- AIR INTAKE FOR FREE PISTON ENGINES 3 Sheets-Sheet 3 INVENTORS United States Patent 2,916,026 AIR INTAKE FOR" FREE PISTON ENGINES William R; Foit; North Riverside;.andRobert H. Wellman, Clarendon Hills, 111., assignors to General Motors Corporation, Detroit, Mich., a corporation 'of Delaware Application Juana; 1958', Serial No. 743,626

6 Claims. ((31. 12346) This invention relates to freepiston engines and more particularly to' sound suppressing air intakes therefor.

Free piston engines: are characterized by two major annoyances which stem from the periodic massive air inhalations of the compressor cylinders during engine operation. The'first'annoyance is high frequency sound which is painful to the hearing and'which'is generated by intake air rushing'through the compressor cylinder intake valves; The second annoyance is low frequency sound which is generated if the'air inhalations take place in a concentrated area and while this low frequency sound is not necessarily painful to the hearing, it can set up wall vibrations in the room which houses the engine. The room and the personnel therein canbe protected against the sound disturbances by surrounding the compressor airintake with duct work extending outside of the room. This form of protection'is not feasible in many casesbecause 'of cost and space limitations and is also objectionable when'habitations are-located in-the immediate areaof theengine'roo'm for suchhabitations are then subjected to the sound disturbances.

An object of the inventionis to provide a free piston engine with an air intake housing for the compressor that will reduce such sound dis'turbances to a tolerable level so that the engine can'be supplied'with air from'theengine room;

The invention provides-a-housing about the compres- 's'or valving-forminga first chamber in communication with the valving and'a second chamber in'cominunicationwiththefir'st chamber'through venturis' andin con-rmunicationwith the room air through'amultitude of small apertures.- The venturi "throat areas are related to the air intake flow of the'engine to obtain substantially sonic air flow between the'chambers'and' thus prevent the high frequency valve sound from escaping the first chamber. The second chamber then spreads-the air in"- take over a considerablearea'Of the' engine room through the multitudeof inlet'apertures to prevent low frequency sound build-up. The air intake through "the apertures may generate some highfrequency sound but this is 'at such a low energy level'as-to'be. readily tolerated.-

Further objects and advantages-of the present invention will be apparent-fromthe-followingdescription, reference being had to the accompanying drawings, wherein a preferred form of the present invention is clearly shown.

In the drawings:

Figure l-is a front elevation, partially broken-away, ofa- Si'am'esedfree piston engine incorporating the inventive air intake;

Figure 2 is an end elevation of-the'air intake taken on the plane-indicated by the line 2.--2:of'Figure 1;

Figure 3 is a perspective of one of the air intake venturis; and

Figure 4 is a partial section through the air intake, taken substantially on the plane indicated by the line 4-4 of Figure 2.

The invention is shown as applied to a free piston or Siamesed with an upper' engine 10'.

gasifier that includes a' lower engine IO'that is paired The illustrated gasifier is '14 feet in length and while such'a size gasifi'er can power a locomotive, it can also make alotof noise. The center portions'ofthe engines 10 and 10 have scavenge air boxes 12 and 12' which communicate witheach other and which'house diesel cylinders (notshown) that exhaust to a turbine (not shown) by way of a common exhaust pipe 14. Compressor cylinders 16 and 16' are secured to the ends of the diesel cylinder air boxes'and each cylinder has a compressor piston 18 reciprocal therein which mounts a diesel piston 20 that is reciprocal in the diesel cylinder, the arrangement providing each engine with opposed free piston assemblies. End covers 22 and'22" close 011 theoutboard ends of the compressor cylinders 16and'16' to provide each compressor piston with'a bounce chamber 24at its outboard side, a compressor chamber 26 being formed by the air box and compressor cylinder at the inboard side. Annular rows of air'intake valves 28 and 28 are mounted in the compressor cylinder walls to supply air to the' compressor chamberson theoutward strokes of the free pistons.

The free pis'ton-gasifier thus described is conventional and operates in the usual'fashion, combustion in the disel'cylinders powering the outward strokes of the pistons, compressing the air in the bounce chambers and drawing air into=the compressor chambers. The compressed air in the bounce chambers powers the inward strokes of the pistons and delivers air under compression from the compressor chambers to the air boxes. The diesel cylindersare fed with compressed air from the air boxes and deliver combustion products under pressure to the turbine when the pistons are in outboard position. During gasifier operation, thepistonsin the lower engine 10 have their outward strokes while the pistons: in the'upper engine 10 have their inward strokes. This dephasing of the upper and lower pistons results in aless fluctuating'flow of exhaust gas to the turbine than would be the casewere the pistons in phaseandalso allows'the upper and'lower compressors to be fed'alternately by a common 'ai'r intakeunit to th'us'iucrease the effective inlet 2 area into the room.

The illustrated-gasifier is designed for normal operation of about 600 cycles per minute for each engine and compressor pistons haveaa 35 inch diameter. It is readily apparent then that the compressor valvesand any room housing. the engine will be subjected to periodic massive air inhalations.. To overcome the resulting soundidisturban'ces notedzearlier, each end of the gasifier-is' provided "with an air intakelassem'bly 30' consisting of housings: 32 forrthe lower engine'and similar housings 32 for theupper engine, the'respective upper and lower housings being inzcommunicationwith'each other;

The housings 32and 32 have peripheral 'walls 34 and 34 secured to the endsof the air boxes 12 and-'12 and extending-"around the cylinders 16' and 16' in spaced relation. End walls 36 and 36 connect the peripheral walls 34 and 34' to the ends ofthecylinders 16-and 16 leavingthe bounce covers-22 and 22 exposed'so the pistons may be removed for maintenance without "disturbing the air inlet assemblies 30: The housings '32and32 also have intermediate sloping partition walls 38 and 38' which extends between the cylinders 16 and16" and the peripheral walls-34 and 34' to form annular chambers Mind 40' and 42 and-42 about the cylinders 16 and 16'. The peripheralwalls '34 and-34' connect'toget-her between the cylinders at 44, the intermediate partition walls 38 and 38 connect together at 46 and the end walls 36 and 36' connect together at 48, thus placing the chambers 40 and 40' in communication with each other and the chambers 42 and 42 in communication with each other.

A plurality of venturi tubes 50 and 50 are mounted in the partition walls 38 and 38 to place the annular chambers 40 and 46' in communication with the annular chambers 42 and 42C. The chambers 40 and 40' contain the intake valves 28 and 28'. A plurality of plates 52 and 52 having a multitude of small apertures 54 and 54 are mounted in the peripheral Walls 34 and 34' to provide an air inlet to the chambers 42 and 42C. The perforated plates 52 and 52 comprise portions of other- Wise conventional air filter assemblies 56 and 56'.

The gasifier is thus supplied with air from the engine room by Way of the intake valves 28 and 28', the compartments 40 and 40, the venturis 50 and 50', the compartments 42 and 42, the multitude of small apertures 54- and 54 and the filters 56 and 56. As noted previously, the engines and 10' are Siamesed and operate with their pistons dephased. The interconnected air inlet housings 32 and 32' are thus utilized to the fullest'extent; since only one compressor piston is on a' suction stroke at any given time. The total throat area of the venturis 50 and 50 is related to the normal intake air flow of the gasifier to result in substantially sonic air flow at the throats. The high frequency, high'energy sound generated by the valves 28 and 28" is thus unable to escape the chambers 40 and 40. The chambers 42 and 42 draw the intake air from the engine room through the multitudinous apertures 52 and 52' which spread the intake over enough of the room area that low frequency vibrations are not set up by the periodic massive air inhalations. The air flow through the apertures may generate some high frequency sound butsuch sound is at such a low energy level as to be readily tolerated. The filters 56 have some sound deadening effect but are primarily provided to function as air cleaners.

While the embodiment of the invention here described is preferred other embodiments may be made within the scope of the invention.

We claim:

1. In a free piston engine having a compressor cylinder with an annular row of air intake valves generating excessive sound during engine operation through periodic massive air inhalations, air intake means for the valves for reducing the sound to a tolerable level comprising a housing assembly enclosing the valve portion of the cylinder and having walls forming first and second chambers and a plurality of venturis in the housing placing the chambers in communication with each other, the first chamber being in communication with the valves and the second chamber having a multitude of small apertures in a'wall thereof communicating with atmosphere.

2. In a free piston engine having a compressor cylinder with an annular row of air intake valves generating 'excessive sound during engine operation through periodic massive air inhalations, air intake means for the valves for reducing the sound to a tolerable level comprising a unitary housing enclosing the valve portion of the cylinder and having walls forming first and second chambers eachproviding an annular space about the cylinder and an annular row of venturis in the housing placing the chambers in communication with each other, the first chamber being in communication with the valves and the second chamber having a multitude of small apertures in a wall thereof communicating with atmosphere.

3. In a free piston engine having a compressor cylinder With an annular row of air intake valves generating eX- cessive sound during engine operation through periodic massive air inhalations, air intake means for the valves for reducing the sound to a tolerable level comprising a unitary housing enclosing the valve portion ofthe 4 cylinder and having Walls forming first and second chambers each providing an annular space about the cylinder, the ends of the cylinder being free of the housing, an annular row of venturis in the housing placing the chambers in communication with each other, the venturis extending in parallel relation with the axis of the cylinder, the first chamber being in communication with the valves, and a plurality of perforated plates and filter elements arranged about the cylinder in a wall of the second chamber placing the chamber in communication with atmosphere.

4. In a Siamesed free piston engine having adjacent compressor cylinders each with air intake valves generating excessive sound during engine operation through periodic massive air inhalations, the inhalations of one cylinder being out of phase with the inhalations of the other cylinder, common air intake means for the valves for reducing the sound to a tolerable level comprising-ahousing enclosing the valve portions of both cylinders and having walls forming first and second chambers and including a plurality of venturis placing the chambers in communication with each other, the first chamber being in communication with the valves of both cylinders and the second chamber having a multitude of small apertures in a wall thereof communicating with atmosphere.

5. In a Siamesed free piston engine having adjacent compressor cylinders each with an annular row of air intake valves generating excessive sound during engine operation through periodic massive air inhalations, the

able level comprising a unitary housing enclosing the valve portions of both cylinders and having walls forming first and second chambers each providing an annular space about both cylinders and an annular row of venturis in the housing placing the chambers in communication with each other, the first chamber being in communication with the valves of both cylinders and the second chamber having a multitude of small apertures in a wall thereof communicating with atmosphere.

6. In a Siamesed free piston engine having adjacent compressor cylinders each with an annular row of air intake valves generating excessive sound during engine operation through periodic massive air inhalations, the inhalations of one cylinder being out of phase with the inhalations of the other cylinder, common air intake means for the valves for reducing the sound to a tolerable level comprising a unitary housing enclosing the valve portions of both cylinders and having walls forming first and second chambers each providing an annular space about both cylinders, the ends of the cylinders being free of the housing, an annular row of venturis in the housing extending in parallel relation with the axis of the cylinder and placing the chambers in communication with each other, the first chamber being in communication with the valves of both'cylinders, and a plurality of apertured plates and filter elements arranged about the cylinder in a wall of the second chamber placing the chamber in communication with atmosphere.

References Cited in the file of this patent UNITED. STATES PATENTS 

